Heat-Shock Protein 70 (Hsp70) Expression in Four Limpets of the GenusLottia: Interspecific Variation in Constitutive and Inducible Synthesis Correlates Within situExposure to Heat Stress

Abstract

Limpets of the genus Lottia occupy a broad vertical distribution on wave-exposed rocky shores, a range that encompasses gradients in the frequency and severity of thermal and desiccation stress brought on by aerial emersion. Using western blot analysis of levels of heat-shock protein 70 (Hsp70), we examined the heat-shock responses of four Lottia congeners: Lottia scabra and L. austrodigitalis, which occur in the high-intertidal zone, and L. pelta and L. scutum, which are restricted to the low- and mid-intertidal zones. Our results suggest distinct strategies of Hsp70 expression in limpets occupying different heights and orientations in the rocky intertidal zone. In freshly field-collected animals and in specimens acclimated at ambient temperature ( approximately 14 degrees C) for 14 days, the two high-intertidal species had higher constitutive levels of Hsp70 than the low- and mid-intertidal species. During aerial exposure to high temperatures, the two low-shore species and L. austrodigitalis exhibited an onset of Hsp70 expression at 28 degrees C; no induction of Hsp70 occurred in L. scabra. Our findings suggest that high-intertidal congeners of Lottia employ a "preparative defense" strategy involving maintenance of high constitutive levels of Hsp70 in their cells as a mechanism for protection against periods of extreme and unpredictable heat stress.

The role of stochastic thermal environments in modulating the thermal physiology of an intertidal limpet, Lottia digitalis

“…Tomanek and Somero, 2002;Huang et al, 2015). It has been previously shown that different limpet species all in the genus Lottia have unique strategies involving heat shock proteins (Dong et al, 2008b). For example, L. scabra maintains high levels of constitutive heat shock proteins whereas L. austrodigitalis, L. scutum and L. pelta rely more on inducing heat shock proteins when exposed to elevated temperatures (Dong et al, 2008b).…”

“…It has been previously shown that different limpet species all in the genus Lottia have unique strategies involving heat shock proteins (Dong et al, 2008b). For example, L. scabra maintains high levels of constitutive heat shock proteins whereas L. austrodigitalis, L. scutum and L. pelta rely more on inducing heat shock proteins when exposed to elevated temperatures (Dong et al, 2008b). It could be that L. digitalis relies more on inducible stress response mechanisms in order to increase thermal tolerance during a specific low tide period as temperatures approach their thresholds of sensitivity.…”

Natural annual cycle of heat shock protein expression in land snails: desertversusMediterranean species ofSphincterochila

“…Interspecific comparisons of ectothermic species from different latitudes have shown that, typically, species adapted to higher temperature niches were more heat tolerant, had higher standing stocks of HSPs, induced the synthesis of HSPs at higher temperatures and had higher upper thermal limits of protein synthesis (Dong et al, 2008;Evgen'ev et al, 2007;Nakano and Iwama, 2002;Tomanek and Somero, 1999;Ulmasov et al, 1992). These studies suggest that organisms occupying extreme environments will employ a 'preparative defense' strategy involving maintenance of high constitutive levels of HSPs in their cells as a mechanism for protection against periods of extreme and unpredictable stress.…”

Triggers of the HSP70 stress response: environmental responses and laboratory manipulation in an Antarctic marine invertebrate (Nacella concinna)

“…The overall expression levels of HSP70B are lower than those of HSP70A under thermal stress, but the response is prolonged. It is possible that the expression levels and control of the HSP70B gene is due to a "preparative defence" mechanism to protect the cells against unpredictable stresses, a continual danger of life in the inter-tidal region (Dong et al 2008). This represents a compromise between the energetics of maintaining a standing stock of HSP transcripts and that required to rapidly induce the genes under stress (Dong et al 2008).…”

“…It is possible that the expression levels and control of the HSP70B gene is due to a "preparative defence" mechanism to protect the cells against unpredictable stresses, a continual danger of life in the inter-tidal region (Dong et al 2008). This represents a compromise between the energetics of maintaining a standing stock of HSP transcripts and that required to rapidly induce the genes under stress (Dong et al 2008). Since the inducible form of HSP70 is present in the form of duplicated genes in N. concinna, this difference in response is both a flexible mechanism for dealing with a variety of environmental insults and logical when viewed in the context of the hypothesis of maintenance of duplicated genes by subfunctionalisation (Force et al 1999).…”